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June 27, 2011 (San Diego) -- A new type of diabetes drug is effective in controlling blood sugar, but it is associated with higher rates of certain infections, researchers say.

The drug, dapagliflozin, is designed to lower blood sugar by increasing the amount of glucose excreted in the urine. On July 19, it will be the first in its class to be evaluated for approval by an FDA advisory committee.

At the annual meeting of the American Diabetes Association, researchers presented results of a two-year study comparing three doses of the drug to placebo, when added to a common diabetes drug, metformin. Another two-year study compared dapagliflozin with glipizide, another common diabetes drug.

The studies showed dapagliflozin led to substantially greater improvements in blood sugar, as measured by hemoglobin A1c (HbA1c) levels, compared with placebo or other diabetes medications.

Patients taking the new drug also lost more weight than those on placebo, but there were more cases of genital and urinary-tract infections as well as of breast and bladder cancer.

Bristol-Myers Squibb Company and AstraZeneca funded the research.

Among the findings:

More patients on the drug than on placebo achieved an HbA1c level of 7% or less, the traditional target of treatment for diabetes patients (20.7% to 31.5% vs. 15.4%).

Patients on placebo gained an average of 3 pounds, while dapagliflozin patients lost an average of 2.4 to 8.4 pounds.

People taking the new drug were less likely to experience episodes of dangerously low blood sugar, known medically as hypoglycemia: 4% to 5% vs. 6% of placebo patients.

Possible Side Effects and Risks

About 12% to 14% of patients being treated with dapagliflozin developed genital infections, compared with about 5% of those taking metformin or placebo. Also urinary tract infection developed in 8% to 13% of patients being treated with dapagliflozin, compared with about 8% of those taking metformin or placebo.

After researchers in one trial saw a couple of cases of cancer among dapagliflozin-treated patients, they reviewed the entire experience with the drug to date. They found nine bladder cancer cases in 5,478 patients on the drug compared with one case in 3,156 people who weren't taking it. They also saw nine breast cancers in 2,223 women on the drug compared with just one in 1,053 women not taking dapagliflozin.

There was no difference in rates of all types of cancer between the two groups.

Since most of the cancers were diagnosed within the first year of the study, it is unlikely the drug caused them, since cancer typically takes years to develop, says researcher Clifford Bailey, PhD, of Aston University in Birmingham, England. Bailey is a consultant to Bristol-Myers Squibb Company and AstraZeneca.

"The numbers [on breast and bladder cancer] are extremely small," Robert Henry, MD, president of medicine and science for the American Diabetes Association, tells WebMD. "There doesn’t seem to be a definite trend." Henry is a consultant to Bristol-Myers Squibb Company and AstraZeneca.

But David Nathan, MD, of Massachusetts General Hospital, says that the observation is worrisome.

Although the researchers "take pains" to suggest these cancers were probably present before drug exposure, follow-up is needed to determine if there is an association between dapagliflozin and cancer, he says.

About a dozen other drugs in this class, known as SGLT2 inhibitors, are in various stages of development.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.